This proposal seeks to investigate the cellular substrates that underlie the experience-dependent reorganization of binocular responses in the mouse primary visual cortex during monocular deprivation. The methods to be used are efficient means of measuring changes in eye-specific responses and neural circuit anatomy longitudinally in individual transgenic mice: (1) transcranial intrinsic signal optical imaging, and (2) two-photon microscopy of calcium indicator fluorescence and genetically labeled neurons. Previous studies have found extragranular layers to be the locus mediating rapid, activity-dependent visual cortical plasticity, with anatomical changes comparable in speed and magnitude to the change in visual responses. In this proposal, this phenomenon will be investigated in greater detail by characterizing the physiological and anatomical changes occurring in vivo in subsets of genetically labeled supragranular excitatory neurons in the binocular zone of the primary visual cortex during monocular deprivation. Since the mouse primary visual cortex is devoid of ocular dominance columns, functional two-photon microscopy will be used to correlate eye-specific responses of singly, genetically labeled neurons with corresponding anatomical changes as they occur during monocular deprivation. The physiological and anatomical changes will be characterized in the context of three temporally distinct phases of monocular deprivation: (1) loss of response to the deprived eye, (2) a dramatic increase in open eye response and a slight increase in deprived eye response, and (3) a return of responses to their initial state after re-opening the deprived eye. The success of this proposal would provide an in-depth understanding of the changes that occur during visual cortical plasticity and could unveil a canvas for future studies investigating the molecular mechanisms that underlie plasticity early in development and in adult. Moreover, elucidating the substrates of visual cortical plasticity is a fundamental issue that supports the basis for treatment of acquired brain abnormalities (e.g. amblyopia).